Semi-automatic rhythm accompaniment



Apnl 19, 1966 D. J. CAMPBELL SEMI-AUTOMATIC RHYTHM ACCOMPANIMENT 3Sheets-Sheet 2 Filed July 9, 1962 HM WNW n m:

m 5 n wrl .SPSw I a? w I $9 @N. k W @N W VN u n mokuwkmo INVENTORDouALoJfAMPBELL BY Z ATTORNEYS April 19, 1966 D. J. CAMPBELL 3,247,309

SEMIAUTOMATI C RHYTHM ACCOMPANIMENT Filed July 9, 1962 3 Sheets-Sheet I5I i i I68 l l I I we Ii 1 INVENTOR IIO H DouALD J CAMPBELL ATTORNEYSUnited States Patent (Mike 3,247,309 SEMI-AUTOMATIC RHYTHM ACCOMPANIMENTDonald J. Campbell, Cincinnati, Ohio, assignor to D. H. 1 BaldwinCompany, a corporation of Ohio Filed July 9, 1962, Ser. No. 208,443 9Claims. (Cl. 84-117) The present application is a continuation-in-partof my co-pending application entitled Rhythmic Interpolation filedAugust 30, 1960 and bearing Serial No. 52,827, now Patent No. 3,140,336.

The present invention relates generally to a musical instrument .forsimulting percussion effects and more particularly to a system forsupplementing certain notes played rhythmically on a musical instrumentby interposing further musical sounds at controlled intervals followingeach of the notes.

In my co-pending application for U.S. patent I have disclosed a systemfor interpolating percussive tones in synchronous relation to the pedalnotes of an electronic organ. The system includes a computer formeasuring a basic time interval between a first pair of pedal notes,establishing a next succeeding basic time interval accordingly, andsub-dividing the latter in accordance with the requirements of a desiredrhythm. Control signals are generated at the termination (and/ orinitiation) of each sub-divided time interval, which are utilized totime interpolated percussive tones. The measurement of each basic timeinterval is stored, to effect control of the duration of the nextsucceeding basic time interval. The subdivided time interval-s in thelatter are thereby controlled, in each musical measure, from theduration of the immediately preceding musical measure. Because of thischaracteristic of the system it is denominated fully automatic.

In the present system, described as semi-automatic, the basic timeinterval, instead of being the result of a measurement, is set into thesystem manually. The initiation of each basic time interval iscontrolled by pedal actuation, but its termination is established by amanual adjustment, in contradis-tinction to the fully automatic systemwherein initiation is controlled as in the semiautomatic system, buttermination is automatically established for one measure from the timingof pedal notes in the immediately preceding measure.

11] playing the electric organ with percussive accompaniment, themusician always actuates a pedal at the commencement of each musicalmeasure. He may play in 34 or time. In the former case a desiredpercussive tone may be an interpolation, for 3Q, time, at thecommencement of a measure and an interpolated percussive tone at thehalf time (second beat) of the measure, or only the latter tone. Fortime, similarly, a percussive tone may be desired at the commencement ofeach measure and an interpolated percussive tone on the second and thirdbeats of the measure, or only on the latter two Ibeats. It is desirablefor the organist to be able to actuate pedals at times other than at thebeginning of a measure without interfering with the interpolated tones.A choice of percussive sounds is also desired, i.e. brush, temple blockand wood block.

In order that the first pedal note of each measure initiate a cycle ofrhythmic interpolation, and that the remaining pedal notes heinoperative for this purpose, a latch is provided. The latch is anamplifier which is gated of during each measure, in response to aninitial pedal tone, and which has as its purpose to initiate a cycle ofoperation in response to the initial or on-beat pedal signal and torender inetlective any subsequent pedal notes played during the measure.

The first negative alternation of a pedal note signal 3,247,309 PatentedApr. 19, 1966 passes through a diode, poled to apply negative controlvoltage to the grid of a latch amplifier. The plate of the amplifier ispulsed positive when its grid goes negative, and the positive pulse isconveyed to a grid of a phantastron, causing the cathode of thephantastron to go negative. The negative potential on the cathodecharges a large capacitor through a diode, and the potential on thecapacitor holds the grid of the latch amplifier negative to cut-off. Thelatch amplifier remains cut oif until after the phantastron cathode goespositive, at the end of the cycle of operations, at which time thecapacitor discharges through a large resistance. The latch amplifierdoes not become conductive and sensitive to further pedal note signalsuntil the capacitor has discharged. Discharge time provides margin timeto allow the organist to play pedal notes on the last after beat. Margintime is caused to increase with decreasing tempo, by associating thedischarge circuit of the capacitor with a tempo control resistance.

The plantastron is conventional, of the cathode coupled type, whose timeof operation is the time between beats, i.e. the reciprocal of tempo.Positive pulses from the latch applied to the suppressor grid of thephantastron tube initiates a phantastron cycle. derived at the end ofeach phantastron cycle are transmitted to a counter, which has thefunction of determining the number of after beats in the rhythm pattern.The counter may be an ordinary :bi-stable multivibrator circuit withsymmetrical input and asymmetrical output. In the case of $4 time thecounter is disabled, and only one pulse is derived from the phantastron,as an after heat. In the case of time the counter is operative to inserttwo after heat pulses, effecting phantastron cycle :for each after beatpulse.

A shaper is employed to convert pulses from the phantastron intoWaveforms suitable for energizing a gated detector and block generator.A switch associated with the phantastron selects the desired rhythmpattern, i.e. with or without on-beat, by selecting a signal outputposition in the phastastron circuit. Negative pulses only are selectedfrom the timer, and these are applied to an amplifier tube grid, causinga rise in plate voltage. The latter voltage charges a capacitor whichthen slowly discharges. The slow discharge provides a sawtooth gatingwave form, which is delivered to a gated detector, to which is alsosupplied noise signal.

The gated detector creates a brushed snare drum sound by shaping theamplitude and spectrum of the noise signal. A block signal generator isalso supplied, which may be selectively applied to an output terminal inplace of the brushed snare drum signal.

It is, accordingly, an object of the present invention to provide asystem .for interpolating rhythmic beats at predetermined points in amusical selection, wherein said interpolation is controlledsemi-automatically.

'It is another object of the present invention to provide a system forsemi-automatically adding rhythmic accompaniment to instrumental musicin timed relation to the music.

Still another object of the present invention is to provide a system forsemi-automatically adding rhythmic accompaniment to electronic organmusic, controlling the initiation of each cycle of accompaniment inresponse to pedal tones of the organ.

It is a further object of the present invention to provide a novelsystem for generating percussion tones for use particularly inelectronic organs.

Still another object of the present invention is to provide a system forgenerating sounds simulating a brushed snare drum, by use of anultrasonic noise signal which feeds a detector through a variableimpedance, the varia- Negative pulses 3 ble impedance varying inaccordance with a predetermined exponential function.

An additional object of the present invention is to provide a novelpulse shaping circuit, utilized particularly in conjunction with aphantastron, for generating output pulses upon the completion of aphantastron cycle of operation.

It is a further object of the present invention to provide a novel waveshaping circuit, responsive to the termination of a phantastron cycle ofoperation, wherein a bias glow tube is supplied with negative voltagespikes from the screen grid of the phantastron tube.

The above and still further objects, features and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed description of one specific embodiment thereof,especially when taken in conjunction with the accompanying drawings,wherein:

FIGURE 1 is a block diagram of a rhythmic interpolator according to thepresent invention;

FIGURE 2 is the circuit diagram of a preferred em bodiment of FIGURE 1;and

FIGURE 3 illustrates wave forms arising in the circuit of FIGURE 2.

Reference is now made to FIGURE 1 of the drawings which discloses asource 11 of oscillations, coupled through an electronic organ pedalswitch 12 to a latch circuit 13. When pedal 12 is closed, the firstoscillation causes latch circuit 13 to supply a signal via 14 tomanually controlled timer circuit 15. In response to the signal on lead14, timer 15 initiates a sawtooth signal having a duration dependentupon a control setting. A blocking signal is fed back from timer 15 tolatch 13, via lead 16, for the duration of the timing signal to preventthe further actuation by signals from source 11.

Upon the completion of the time interval for which timer 15 has beenpreset, a signal is transmitted to counter 17 via lead 18, from timer15. The signal on lead 18 causes counter 17 to switch states. Thisresults in the application of a control signal to timer 15 via lead 19from counter '17, which re-instigates the timing cycle of timer 15. Whenthe timer cycle is re-instigated, latch 13 is again blocked via lead 16,and cannot respond to closure of pedal switch 12. When timer 15 hascompleted its cycle in response to the signal applied to it via lead 19,a further pulse is applied to counter circuit 17 via lead 18. Thisfurther pulse resets counter circuit 17 to its original state.Accordingly, timer 15 is cycled through two predetermined time periodcycles in response to closure of switch 12. For 4 tempo, counter 17 isdisabled and generates no output pulses in response to transitions inthe timer cycle, whereby the timer goes through only one cycle inresponse to a closure of switch 12.

The duration of each of the cycles is determined manually in accordancewith a manually controlled tempo setting. The tempo setting may causebeats to be produced at a rate of between 60 to 300 per minute. Inresponse to the initiation and end of each timing cycle, a pulse isgenerated on lead 21, while pulses are derived on lead 22 only inresponse to the end of each timing cycle.

The signals on leads 21 and 22 are selectively applied to shaper 23 viaswitch 24 and lead 25. Shaper 23 transforms the sharp pulses on lead 25into slowly decaying wave forms, which have decayed completely in a timeperiod equal to the periodicity of timer 15. The output of shaper 23 isapplied in parallel to block generator 26 and gated detector 27. Blockgenerator 26 supplies, in response to the leading edge of the outputfrom shaper 23, -a shock excited, highly damped sinusoidal wave. Thefrequency of the wave derived from block generator 26 is commensuratewith that produced by a temple or wood block. Detector 27, in additionto being supplied with the damped exponential output of shaper 23, isresponsive to a noise source 28. Shaper 23 controls the detection of thenoise provided by noise source 28 as it is fed through instrument.

Reference is now made to FIGURE 2 of the drawings, wherein isillustrated a circuit diagram of a preferred form of the system ofFIGURE 1. Latch circuit 13 includes a first triode 31 having its gridelectrode 32 responsive to the negative input signal applied to inputterminal 33 via diode 34 and bias capacitor 35. The junction between theanode of diode 34 and one plate of capacitor 35 is coupled to loadresistor 36, for diode 34. The junction between input terminal 3 and thecathode of diode 34 is connected to signal load resistor 37 at one ofits terminals, the other terminal of resistor 37 being connected toground. Tube 31 is normally maintained in the conducting state by thecathode biasing circuit, which includes resistors 38 and 39 connected inseries as a voltage divider for positive DC. potential connected toterminal 41. The junction between resistors 38 and 39 is connected tobypass capacitor 42 and the cathode 43 of triode 31. The plate 44 oftriode 31 is connected through plate load resistor 45 to B+ terminal 46.i

The output signal of the triode 31 is coupled via blocking capacitor 47to the suppressor grid 48 of pentode 49, connected in a phantastronconfiguration. Suppressor grid 48 is normally maintained at cutoif by abiasing circuit which includes voltage dividing resistors 51 and 52,which are connected between ground and a positive source of DC. biasingvoltage. Connected in parallel with resistor 52 and to the suppressorgrid 48 is capacitor 53, which maintains the proper suppressor bias andprevents the application of excess currents to the suppressor.

Pentode 49 is the essential element of a phantastron circuit whichincludes cathode follower circuit 54. Plate 55 of pentode 49, inaddition to being connected to the B+ source via plate load resistor 56,is connected to the grid 57 of cathode follower triode 54. Anode 58 oftriode 54 is connected directly to a source of B+. Cathode electrode 59is connected to load resistor 61 and to the control grid 62 of pentode49 via integrating capacitor 63.

Control grid 62 is normally maintained above cutoff by the biasingpotentiometer 64, which is series connected to voltage limiting resistor65. One end of potentiometer 64 is connected to a positive voltageterminal so that the slider 66 thereof couples a positive DC. voltage tothe control grid 62 via current limiting resistor 67 which is connectedto the slider 66. Cathode 68 of pentode 49 is connected to ground by acathode load resistor 69. When the suppressor grid 48 of tube 49 ismaintained at cut-off, a current path exists between cathode 68 andcontrol grid 62 and screen grid 71. This current is of appreciable valueso that when the phantastron plate current is cut off there is apositive DC. voltage across resistor 69.

The voltage across resistor 69 is coupled to the grid 32 of triode 31via diode 72 Cathode resistor 69 is connected to the cathode of diode72, the anode thereof being connected to the junction between capacitor35 and grid 32. Slider 66 of potentiometer 64 normally couples apositive D.C. biasing voltage to the control grid 32 via a large currentlimiting resistor 73.

The timer circuit 15, including pentode 49 and triode 54, is connectedas a normal phantastron circuit, the triode being included to insurerapid flyback after bottoming has occurred in pentode 49.

The negative output derived at the screen grid 71 of pentode 49 at theend of each timer cycle is applied to a shaping circuit 74. The screengrid 71 is maintained at a positive bias by the DC. voltage connected toterminal 75 and screen load resistor 76.

Clipping circuit 74 includes a differentiator comprising capacitor 77and resistor 78-, the former being connected directly to the screen gridand the latter to ground. The junction between capacitor 77 and resistor78 is connected to one terminal of neon glow tube 79, the other terminalof which is connected to a biasing circuit which includes voltagedivider resistors 81 and 82. Voltage divider resistors 81 and 82 areconnected in series between a positive voltage source which is ofinsufficient voltage to ignite tube 79.

The clipping circuit output is coupled to the input of counter 17 viacoupling capacitor 83. Counter 17 comprises a standard plate fedflip-flop or frequency dividing circuit. Flip-flop 17 includes a set ofdual triodes 84 and 85 which have their plate resistors 86 and 87connected to capacitor 83 and a common load resistance 88 which is D.C.coupled to a source of B+. Counter 17 is a standard bistablemultivibrator circuit including cross-coupling circuits 89 and 91connected between the anodes and grids of the respective tubes.

A cathode biasing circuit for tubes 84 and 85 is provided so that tube84 is normally maintained in the conducting state. The biasing circuitincludes the parallel combination of resistor 92 and capacitor 93,connected between the cathodes of tubes 84 and 85 and ground andresistor 94, the latter being shunted by switch 95.

When the circuit of the present invention is utilized for time, switch95 is closed so that normal flip-flop operation occurs. For 4 time,switch 95 is open to disable the counter. Disabling occurs because ofthe high value of resistor 94 compared to resistor 92.

The output of counter 17 is derived from the plate of triode 84 andapplied to delay circuit 96. Delay circuit 96 includes an integratingcircuit consisting of resistor 97, connected to the counter output, andcapacitor 98. A pair of neon glow tubes 99 and 101 are series connectedbetween the integrator output and the input to a differentiator whichincludes resistor 102 and capacitor 103. The'output of delay circuit 96taken across the differentiator is applied to the suppressor grid 48, ofthe phantastron pentode.

The output of phantastron tube 49 is selectively derived across thecathode load resistor 69 or the screen grid shunting. capacitor 104 bycontrol of switch 24. Cathode load resistor 69 is connected to onecontact of switch 24 and lead 21 by way of a differentiating circuitwhich includes capacitor 105 and resistor 106, the latter beingconnected to ground. The screen grid output is obtained by positioningswitch 24 so that it contacts resistor 107 which is series connected toscreen grid 71 by way of capacitor 108. With switch 24 engaging lead 21and cathode 68, an output pulse is derived from the timer circuit inresponse to the initial application of a signal to terminal 33 and theoccurrence of the trailing edges of the waves generated by the timer. Incontrast, no signal is derived from lead 22 when an input is appliedinitially to terminal 33, an output being derived at lead 22 only inresponse to the termination of the timing waves.

The signal at switch 24 is applied to the control grid of triode 100which is included in shaper 23. The control grid is connected to a gridleak resistor 110, the other end of which is connected to ground.Connected to the oath ode of triode 100 is a cathode biasing resistor1119. Connected to the anode of this tube is plate load resistor 111which is coupled to the triode source of B+.

The output at the plate of triode 100 is D.C. coupled to the grid ofcathode follower triode 112. The anode of triode 112 is connected to B+and the cathode thereof is connected to a shaping circuit which isessentially a low pass filter. The shaping or filter circuit includescapacitor 113, connected between the cathode of tube 112 and ground,resistor 114, and shunting capacitor 115. The shaping circuit output iscoupled via a pair of current limiting and voltage attenuating resistors116 and 117 and brush control switch 118 to the control grid of tube119,

included in gated detector 27. The input signal for triode 119 isgenerated across grid leak resistor 121 which is responsive to theoutput of the shaper and noise source 28.

Noise source 28 includes a conventional Hartley oscillator, having aresonant frequency of about 500 kc. The oscillator includes a tankcircuit including capacitor 121 connected in parallel with tapedinductance 122 and resistor 123. The tap of inductor 122 is connected tothe cathode of triode 124, the grid of which is connected to one end ofcoil 122 via a quenching circuit which in cludes capacitor 125 andresistor 126. Capacitor 125 is series connected between one end ofinductance 122 and the control grid of triode 124 while the resistance126 is connected between the control grid and ground. The output of theHartley oscillator is derived at its plate which is connected to a B[source via load resistance 127.

The oscillations at the anode of triode 124 have three separatecomponents, a high amplitude 25 kc. sawtooth wave which is amplitude andfrequency modulated with wide band audio noise; the 500 kc. oscillationsset up by the Hartley oscillator and a low amplitude wide band thermaland tube noise signal. The 25 kc. sawtooth oscillations are establishedby the quench circuit, including resistor 126 and capacitor 125, whichalternately gates tube 124 on and off in a known manner similar tosuperregenerative oscillator operation.

The output of tube 124 is applied to the control grid of triode 119 viaa band pass filter 128. Filter 128 includes an RF bypass capacitor 129which is directly connected in shunt with the anode of triode 124 and ahigh pass filter which includes a pair of cascaded capacitanceresistance sections. The first section includes capacitor 131, directlyconnected to the anode of tube 124 and resistor 132, connected to theother side of capacitor 131 and ground. The second section of thecascaded filter includes capacitor 133 which is connected betweenresistor 132 and the grid of tube 119 and resistance 121.

Thus, the outputs of shaper 23 and noise source 28 are combined in gateddetector 27. The amplitude of the signal applied to the gated detector27 from shaper 23 varies the impedance of triode 119 to effect avariable detection of the noise source output.

The plate of detector 119 is connected to B+ source via series connectedresistances 222 and 223 the junction of which is connected to the slider224 of potentiometer 225 via dropping resistor 226. Triode 119 isnormally maintained at cutoff by the cathode biasing circuit includingcapacitor 227 which is connected to slider 224, since one end ofpotentiometer 225 is connected to a positive voltage source. Connectedin shunt with the anode of triode 119 is detecting capacitor 228 and ashaping circuit which includes the series combination of capacitor 229and potentiometer 231.

The slider of potentiometer 231 is connected to a control circuit whichincludes capacitor 232 and resistance 233 which is coupled to thecathode input resistor 234 of triode 235 which serves as the outputamplifier of the rhythmic interpolator circuit. The grid of triode 235is supplied with signals from block generator circuit 26 which is alsofed by the output of triode 100.

The plate output of tube 108 is coupled through a pair of seriesconnected neon glow tubes 137 and 138 to a shaping circuit wihchincludes capacitor 139 and resistors 141 and 142. The shaping circuitoutput is applied to a highly damped shock excited generator by diode143.

The shock excited generator includes the parallel combination ofcapacitor 144 and coil 145 which are tuned to a suitable frequency forsimulating the tone of a wood block'being struck with a drum stick.Connected between coil 145 and capacitor 144 is switch 146 which isclosed when it is desired to simulate the block sound.

A further switch .147 is connected to capacitor 144 so that capacitor148 is selectively connected in parallel with the capacitor 144. Whenswitch 147 is closed and capacitor 148 is connected in parallel withcapacitor 144 the resonant frequency of the shock excited circuit isdecreased so that tones simulating a temple block are simulated. Closureof switch 147 also results in an amplitude compensation of the shockexcited oscillations which are applied across potentiometer 149 byresistor 151 when switch 147 is open. Resistor 152, having a smallervalue than resistance 151, couples the shock excited wave to thepotentiometer with switch 147 closed. The selection of resistors 151 and152 is dependent upon the decrease in amplitude of the shock excitedwave when capacitor 148 is included in the circuit.

The output of block generator 26, obtained at the slider ofpotentiometer 149, is coupled to the control gride of triode 135. Ifswitch 118 is closed at the same time switch 146 is closed, the audiofrequency signals applied to the grid and cathode of triode 135 arecombined in a linear manner in a manner quite like that of combinedbrush and block drum beat. The oscillations applied to triode 135 areamplified in the output circuit which includes plate load resistor 153which is connected to a suitable source of B+ and decoupling capacitor154.

Reference is now made to FIGURES 2 and 3 for a description of the mannerin which the circuit of the present invention functions. Initially themusician operating the instrument sets the various controls to thedesired states. Switch 95 is open if it is desired to have a drum beatfor time music while it remains in its closed position for A time.

Potentiometer slider 66 of potentiometer 64 is rotated to theappropriate tempo at which the music is to be played. For fast tempowhen the phantastron timing period must be maintained at a shortduration, slider 66 is positioned so that a large positive voltage isapplied to the grid 62 of pentode 49 so that bottoming of thephantast'ron cycle will occur fairly soon after initial suppressoractivation. For slower tempos, slider 66 is moved towards the lower endof potentiometer 64 and the period of the phantastron is increased.

If it is desired to produce a percussion sound with the initial closureof the pedal switch, switch 24 is coupled to lead 21 so that an outputis derived across the cathode load resistor 69 of pentode 49. If to thecontrary, no percussion sound is desired at initial pedal activation,termed no on-beat, switch 24 is rotated to engage lead 22 and an outputis derived from the screen grid of pentode 49.

For brush simulated sounds, switch 118 is closed so tnode 119 may beperiodically rendered in a conductive state by the output of shaper 23.T provide drum beats similar to a wood block, switch 146 only is closedwhile both switches 146 and 147 are closed for simulation of a templeblock sound. To control the volume of the sounds which are derived fromthe unit, the sliders of potentiometers 131 and 149 are rotated to anappropriate position for the desired loudness of the brush and blocksounds, respectively.

Upon closure of the pedal switch which generally occurs at least onceevery measure in popular or jazz music, wave form 161, FIGURE 3, isapplied to the cathode of diode 34. In response to a negative excursionof wave form 161, a negative voltage is applied through diode 34 to grid32 of tube 31, causing plate 44 of tube 31 to go positive.

The sudden increase of plate voltage of tube 31 is applied throughcapacitor 47 as pulse 163a, Wave form 163, to the suppressor grid 48 ofpentode 49. This results in a sudden flow of plate current in pentode 49with a corresponding sudden decrease at the grid 62 because of thevoltage drop through capacitor 63. The voltage drop at grid 62 resultsin a decrease in the cathode current and a correspondingly negativeswing across cathode load resistance 69, as indicated by wave form 164.

The negative swing across cathode load resistance 69 is applied throughdiode 72 to charge capacitor 35. The

grid 32 of triode 31 is held negative by the charge on capacitor 35 tolatch the triode into a cutotf state, so that further application ofwave forms 161 to terminal 33 does not effect tube 31. The negativevoltage applied through diode 72 is stored in capacitor 35 to positivelyprevent the positive sinusoidal swing of wave form 161 from reaching thegrid of triode 31.

In accordance with the well-known operation of a phantastron circuit,the plate voltage of pentode 49 and the cathode voltage of triode 54decrease linearly, as indicated in wave form 166. When plate currentsaturation occurs, and capacitor 63 stops discharging, a suddenregenerative termination of plate current occurs resulting in a sharpincrease of plate voltage.

Prior to the occurrence of pulse 163a on suppressor grid 48 of pentode49, considerable current flows through screen grid 71 causing the screento be maintained at a relatively low potential. Upon the occurrence ofpulse 163a and the ensuing flow of plate current in pentode 49, thescreen current decreases suddenly causing an increase screen voltage,'asindicated by wave form .167. In response to plate current cutoff inpentode 49, the screen grid voltage suddenly decreases to its formervalue.

The positive and negative going wave forms derived at the screen grid 71are applied to differentiator 'circuit which includes capacitor 77 andresistor 78. The difi'erentiator output consists of positive andnegative going spikes, as indicated by wave form 168. The positive goingspike has no effect on neon glow tube 79 and accordingly is not passedto the voltage divider which includes resistors 181 and 182. However,the negative going spike in wave form 168 instantaneously fires neonglow tube 79. Thereby a negative spike, as indicated by wave form 169,is derived at the junction between resistors 81 and 82 in response tocutoff of plate current in pentode 49.

The negative going pulse, indicated by wave form 169, is applied to theflip-flop or counter stage 17 which includes tubes 84 and 85. Tube 84,normally maintained in the conducting state, is cutoff in response tothe negative pulse, thus rendering tube 85 conductive. In response tocut-off of tube 84, a sudden increase of its plate voltage occurs, asindicated by wave form 170.

The step voltage derived from. the plate of triode 84 is applied to anintegrating circuit which includes resistor 97 and capacitor 98. Theintegrator smoothes the sudden plate voltage increase so that wave form171 is applied to series connected neon glow tubes 99 and 101.Accordingly, glow tubes 99 and 101 do not fire until a predeterminedtime interval after the occurrence of a negative going spike in waveform 169.

When the voltage across integrator capacitor 98 has reached thenecessary level to fire neon glow tubes 99 and 101, a positive pulse isderived at the junction between resistor 102 and capacitor 103, asindicated by wave form 172. The sudden increase in voltage at thejunction between resistor 102 and capacitor 103 results in theapplication of another positive pulse to the suppressor grid 48 ofpentode 49. This reinstigates the cycle which has just previously beencompleted so that triode 31 is again cut off and .a positive voltage isapplied to the differentiator which consists of capacitors 77 andresistors 78. It will be seen that the inclusion of the delay circuit 96is necessary to insure .a suflicient time delay between the cutoff ofpentode 49 and the beginning of a second cycle.

When phantastron plate current ceases to flow during the second timingcycle, another negative voltage is applied to the plates of triodes 84and 85 of counter 17 so that triode 84 is rendered conductive. Thereby,the plate voltage wave form decreases to its former value and gas tubes101 and 99 are extinguished. This results in a sudden decrease involtage to the terminal between capacitor 1193 and resistor 1152. Thenegative voltage has no effect on the phantastron operation, however,since the suppressor grid 48 is normally biased to cutoff. The negativevoltage only has the effect of further driving grid 48 momentarilybeyond cutoff.

Upon completion of the second cycle, the voltage across cathode resistor69 increases suddenly. This sudden increase in voltage at the cathode ofpentode 49 causes diode 92 to cut off, resulting in a subsequentdischarge of capacitor 35 through resistor 73, as indicated by wave form165. Triode 31 is then ready to be reactivated in response to a negativeinput to terminal 33 to reinitiate the cycle of operation.

With switch 24 engaging lead 22, the wave form 167 at the screen grid 71of pentode 49 is applied through the shaping network, which includesresistor 107 and capacitor 168, to the grid of triode 100. In responseto the positive and negative going wave forms 167, positive and negativegoing spikes, respectively, are derived, as indicated by wave form 173.The positive going spikes derived in response to the initiation of aphantastron cycle have no effect on triode 100 since it is normallymaintained in a fully conducting state. However the negative goingspikes are amplified by the circuitry of triode 1610 so that the pulsesindicated by wave form 174 are derived at the plate of triode 190. Apulse is derived at the end of each phantastron cycle when switch 24-engages lead 22.

When switch 24 engages lead 21 and the cathode voltage of pentode 49 isapplied to the grid of triode 100, a negative spike, as indicated bywave form 173", is applied to the triode in response to the beginningand completion of each phantastron cycle, the spikes being derived dueto the differentiating action of capacitor 105 and resistor 106. Thesenegative spikes result in a pulse being derived at the plate of triode100 in response to both the initiating pedal switch closure and to theend of each phantastron cycle.

capacitor 113 is rapidly charged by triode 112 and is slowly dischargedthrough resistors 114, 116, 117, and 121.

Wave form 175", is attenuated by the voltage divider made up ofresistors 114, 116, 117, and 121 and slightly smoothed by relativelysmall capacitor 115 to produce wave form 1'7 6". This wave form isapplied to the grid of normally cutoff triode 119 in the gated detector27. When the grid voltage achieves a sufficiently high level, tube 119is rendered conductive thereby passing varying segments of the output ofnoise source 28. Tube 119 therefore acts as a rectifier to pass onlyportions of the noise source above varying levels which depend on theamplitude of the shaper output. As described supra, noise source 28generates an output having three components, the most predominant ofwhich is a 25 kc. sawtooth which is A.M. and FM. modulated with wideband audio noise. The ultrasonic output of noise source 28 is applied tothe grid of triode 119 and its envelope is detected by capacitor 228.The resistance of tube 119 is varied in response to the exponential waveform 176" so that the driving impedance of detector capacity 129 isamplitude modulated in a preselected manner by wave form 176. Theamplitude modulations from noise source 28 on the ultrasonic carrier,when subjected to the amplitude modultion and variable detectionintroduced from shaper 23, results in a signal at the output of thedetector which closely simulates the sound of a brushed snare drum,because its frequency spectrum and amplitude vary in a desirable mannerin response to the 10 gating valve form 176". The brush signal isapplied to the cathode of triode 235 so that an amplified output signalis derived at the plate resistance 253.

In response to positive pulses at the plate of triode 100, neon glowtubes 137 and 138 are fired instantaneously so that a positive spike ispassed through capacitor 139 and diode 143 to the shock excited tankcircuit which comprises capacitor 144 and inductance 145. This highlydamped shock excited wave simulates the sound of a wood block beat whenswitch 147 is open. Upon closure of switch 147 capacitor 148 is added inthe tank circuit thereby reducing its natural resonance frequency sothat a wave corresponding with a temple block beat occurs. This wave isalso damped to a great extent due to resistance 152 and potentiometer149. The damped sinusoidal oscillations applied to the grid of triode135 are suitably amplified so that a voltage simulating block beat isderived at the system output terminal.

The preceding description of the functioning of the present device wasbased upon the assumption that switch was closed so that time percussionsounds are derived. With 4 time, switch 95 is open and no output pulsesare .derived from counter 17. Accordingly, the second cycle ofphantastron operation does not occur and the number of pulses at theplate of triode is reduced by one for each closure of the pedal switch.

While I have described and illustrated one specific embodiment of myinvention, it will be clear that variations of the details ofconstruction which are specifically illustrated and described may beresorted to Without departing from the true spirit and scope of theinvention as defined in the appended claims.

In the claims:

1. A system for simulating percussion sounds, comprising a source ofultrasonic signals modulated in frequency and amplitude by audiofrequency noise, a normally disabled gated detector connected in cascadewith said source, a source of shaped gating voltages recurring at adesired recurrence rate of said percussive sounds, said gating voltageseach having a relatively rapid rise and relatively slow exponentialfall, and means applying said gating voltages to said gated detector inenabling relation, whereby shaped bursts of detected versions of saidultrasonic signals are passed by said detector, and an electroacoustictransducer responsive to said shaped bursts of V detected versions ofsaid ultrasonic signals.

2. In a system for simulating the sound of a brushed snare drum, meansfor generating an ultrasonic carrier modulated in frequency andamplitude by wide band audio noise, a gated' detector responsive to saidcarrier to generate a noise signal, means for gating said detector toform a detected signal of predetermined shape simulating the acousticshape of a brushed snare drum sound in response to said carrier, and anelectro-acoustic transducer responsive to the detected signal.

3. A system for simulating percussive sounds of a brushed snare drum,comprising a source of ultrasonic carrier modulated by audio frequencynoise, a gated detector for detecting the modulation of said carrier,said detector comprising an ormally disabled rectifier having a variabledetection level in accordance with the amplitude of a gating wave, and asource of said gating wave coupled in enabling relation to saidrectifier, said gating wave coupled in enabling relation to saidrectifier, said gating wave having a wave shape appropriate tosimulation of sounds of a brushed snare drum.

4. The combination according to claim 3 wherein said source comprises asinusoidal oscillator, and a circuit coupled to said sinusoidaloscillator for quenching its oscillations at an ultrasonic rate.

5. In a sonic system, a source of signal bursts having variablespacings, said signal bursts being alternating current signal bursts,means responsive to the initial cycle only of each of said bursts forgenerating a control pulse,

means for at will manually establishing controllable time intervals atleast approximately equal to the time interval between adjacent ones ofsaid bursts and commencing at and in response to each pulse, means formusically subdividing each of said time intervals to providesub-intervals and providing a further control signal at the terminationof each sub-interval, and means responsive to said further controlsignals for generating simulated percussive sounds, said last meanscomprising a source of ultrasonic signals modulated in frequency andamplitude by audio frequency noise, a normally disabled gated detectorconnected in cascade with said source, a source of shaped gatingvoltages recurring at a desired rhythm of said percussive sounds, saidgating voltages each having a relatively rapid rise and a relativelyslow exponential fall, and means applying said gating voltages to saidgated detector in enabling relation, whereby shaped bursts of detectedversions of said ultrasonic signals are passed by said detector, and anelectro-acoustic transducer responsive to said shaped bursts of versionsof said ultrasonic signals.

6. In a sonic system, a source of signal bursts having variablespacings, said signal bursts being alternating current signal bursts,means responsive to the initial cycle only of each of said bursts forgenerating a control pulse, means for at will manually establishingcontrollable time intervals at least approximately equal to the timeinterval between adjacent ones of said bursts and commencing at and inresponse to each pulse, means for musically subdividing each of saidtime intervals to provide sub-intervals and providing a further controlsignal at the termination of each sub-interval, and means responsive tosaid further control signals for generating simulated percussive sounds,said last means comprising means for generating an ultrasonic carriermodulated in frequency and amplitude by wide band audio noise, a gateddetector responsive to said carrier to generate a noise signal, meansfor gating said detector to form a detected signal of predeterminedshape simulating the acoustic shape of a brushed snare drum sound inresponse to said carrier, and an electro-acoustic transducer responsiveto the detected signal.

7. In a sonic system, a source of signal bursts having variablespacings, said signal bursts being alternating current signals bursts,means responsive to the initial cycle only of each of said bursts forgenerating a control pulse, means for at will manually establishingcontrollable time intervals only approximately equal to the timeinterval between adjacent ones of said bursts and commencing at and inresponse to each pulse, means for musically subdividing each of saidtime intervals to provide sub-intervals and providing a further controlsignal at the termination of each sub-interval, and means responsive tosaid further control signals for generating simulated percussive sounds,said last means comprising a brushed snare drum, comprising a source ofultrasonic carrier modulated by audio frequency noise, a gated detectorfor detecting the modulation of said carrier, said detector comprising anormally disabled rectifier having a variable detection level inaccordance with the amplitude of a gating wave, and a source of saidgating wave coupled in enabling relation to said rectifier, said gatingwave having a wave shape appropriate to simulation of sounds of abrushed snare drum.

8. In a sonic system, a source of signal bursts having variablespacings, said signal bursts being alternating current signal bursts,means responsive to the initial cycle only of each of said bursts forgenerating a control pulse, means for at will manually establishingcontrollable time intervals at least approximately equal to the timeinterval between adjacent ones of said bursts and commencing at and inresponse to each pulse, means for musically subdividing each of saidtime intervals to provide sub-intervals and providing a further controlsignal at the termination of each sub-interval, and means responsive tosaid further control signals for generating simulated percussive sounds,said last means comprising a sinusoidal oscillator, and a circuitcoupled to said sinusoidal oscillator for quenching its oscillations atan ultrasonic rate.

9. In a sonic system, a source of signal bursts having variablespacings, said signal bursts being alternating current signal bursts,means responsive to the initial cycle only of each of said bursts forgenerating a control pulse, means for at will manually establishingcontrollable time intervals at least approximately equal to the timeinterval between adjacent ones of said bursts and commencing at an inresponse to each pulse, means for musically subdividing each of saidtime intervals to provide sub-intervals and providing a further controlsignal at the termination of each sub-interval, and means responsive tosaid further control signals for generating simulated percussive sounds,said last means comprising a resonant circuit having a relatively rapiddecay time, a source of pulses recurrent at a sub-audio rate, saidpulses being of relatively short durations and relatively longinterpulse spacings, said resonant circuit being responsive to each ofsaid pulses, said resonant circuit being tuned to a frequency and havinga decay time appropriate to simulation of a wood block sound, and anelectro-acoustic transducer coupled to said resonant circuit, wherein isfurther provided circuitry for modifying the frequency of said resonantcircuit to a frequency appropriate to the sounds of temple blocks, andmeans for at will connecting said circuitry to said resonant circuit.

References Cited by the Examiner UNITED STATES PATENTS 2,432,152 12/1947Hanert et a1. 841.19 2,461,266 2/ 1949 Gay 328 2,697,959 12/1954 Kent84l.22 2,855,816 10/1958 Olson et al. 841.03 2,926,246 2/ 1960 Bivens328130 2,941,435 6/1960 Henley 841.22 3,105,106 9/1963 Park 84-1.03

GEORGE N. WESTBY, Primary Examiner.

1. A SYSTEM FOR SIMULATING PERCUSSION SOUNDS, COMPRISING A SOURCE OFULTRASONIC SIGNALS MODULATED IN FREQUENCY AND AMPLITUDE BY AUDIOFREQUENCY NOISE, A NORMALLY DISABLED GATED DETECTOR CONNECTED IN CASCADEWITH SAID SOURCE, A SOURCE OF SHAPED GATING VOLTAGES RECURRING AT ADESIRED RECURRENCE RATE OF SAID PERCUSSIVE SOUNDS, SAID GATING VOLTAGESEACH HAVING A RELATIVELY RAPID RISE AND RELATIVELY SLOW EXPONENTIALFALL, AND MEANS APPLYING SAID GATING VOLTAGES TO SAID GATED DETECTOR INENABLING RELATION, WHEREBY SHAPED BURSTS OF DETECTED VERSIONS OF SAIDULTRASONIC SIGNALS ARE PASSED BY SAID DETECTOR, AND AN ELECTROACOUSTICTRANSDUCER RESPONSIVE TO SAID SHAPED BURSTS OF DETECTED VERSIONS OF SAIDULTRANSONIC SIGNALS.